Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$242.59	11.506%	$270.5024	$270.50	$270.50	$270.50
Purchase #2	$87.31	13.123%	$98.7677	$98.77	$98.75	$98.80
Purchase #3	$38.78	7.421%	$41.6579	$41.66	$41.65	$41.70
Purchase #4	$92.40	12.767%	$104.1967	$104.20	$104.20	$104.20
Purchase #5	$158.84	5.682%	$167.8653	$167.87	$167.85	$167.90
Purchase #6	$70.72	10.766%	$78.3337	$78.33	$78.35	$78.30
Purchase #7	$184.52	3.771%	$191.4782	$191.48	$191.50	$191.50
7 purchase totals =	$875.16		$952.8019	$952.81	$952.80	$952.90